AbdulAlhazred
Legend
Well, presumably, all these characters are compatible in that they all interact with combat in the same way. It's not like you'd have 2e characters and 3e characters in the same fight. It's just that characters built with Advanced Combat Maneuvers module would be more powerful than characters built without it. A party of level 4 ACM characters might face the same xp budget as a party level 6 basic characters. (Of course, there could be ACM monsters who have more complicated powers that are worth more xp...)
Some modules might allow the PCs to interact with different sub-systems. For example, a kingdom management module might provide a new "silo" where each character gets new powers that are principally useful when interacting with the kingdom rules.
Other modules just add to the power of the characters. For example, you could imagine a Book of Themes (ok, I'd imagine a better name). If the group wants mechanical support for themes, then everyone gets extra powers and the effective level of the party goes up by 1.
-KS
"Queen of the Demented Hips: A module for 4|6/7 characters of levels 12-16|6-8/9-12*"
*note: not recommended to be used with the Epic Magic supplement, requires the Advanced Tactics supplement. Some errata required to play with version 1.0 of the Skills and Powers supplement.
sigh.